1. Field of the Invention
This invention relates to a mouse interface converter, and more particularly, to a mouse interface converter that allows a mouse (pointing device) to be connectable to a computer system, such as a personal computer (PC), installed with either an RS-232 serial port or a PS/2 port.
2. Description of Related Art
Modem computers typically utilize a graphic-based operating environment, called graphical user interface (GUI), for the user to operate the computer in a very user-friendly manner with a point device, such as a mouse or the like. The user can select and activate options simply by pointing and clicking with the mouse. With the earlier technology, a mouse is connected to a PC via a dedicated interface card. One drawback to the use of the dedicated interface card is that it is quite laborious to install in the PC and requires additional power supply to operate. Newer technology allows the mouse to be connected to the PC via the standard RS-232 serial port without the need of additional power supply. However, a single PC unit typically comes with only two RS-232 serial ports, and typically the total number of external devices that need to be connected via RS-232 serial ports to the PC is often more than two. These external devices include, for example, a MODEM (abbreviation for modulator-demodulator, which is used to connect the PC to a network, such as INTERNET) and an infrared transmitter. Therefore, with the addition of a mouse that also requires the RS-232 serial port for connection to the PC, the user may be frequently involved in repeated unplugging and plugging of the various devices to the PC, which is, needless to say, very laborious and inconvenient.
Moreover, on portable computers, such as notebook computers, a new interface called PS/2 interface is provided for the computer to connect a mouse thereto. The PS/2 interface is now also standard on some newer models of desktop PCs.
The RS-232 interface and the PS/2 interface are distinctively different in specifications. Presently, most mouse devices on the market can be connected to one type of port only, either the RS-232 serial port or the PS/2 port, but not both. Therefore, when purchasing a new mouse, the user must know which type of port his/her PC comes with, and then purchase the mouse that is specifically designed to be connectable to that type of port; otherwise, if a wrong type of mouse is purchased, it would not be able to operate properly. Ordinary users, however, are typically unaware of such distinctions. Moreover, not all PCs come with both the RS-232 serial port and the PS/2 port together on the same unit, typically with one of them only. A PC with the RS-232 serial port will be unable to use a PS/2-compliant mouse; and similarly, a PC with the PS/2 port will be unable to use an RS-232-compliant mouse. There exists, therefore, a need in the PC market for means that allows a mouse to be connectable to a PC installed with either an RS-232 serial port or a PS/2 port. One solution to this need is to use an adapter.
FIGS. 1A-1B are schematic diagrams used to depict a conventional solution that allows a mouse to be connectable to a PC with either an RS-232 serial port or a PS/2 port. As shown in FIG. 1A, assume the mouse 120 is PS/2-compliant, i.e., which is specifically designed for direct connection via a PS/2 port 111 to a PC 110. In this case, the mouse cable 121 can be directly connected between the mouse 120 and the PS/2 port 111.
When it is desired to connect the mouse 120 to a PC 110 with an RS-232 serial port 112, an adapter 130 is used to connect between the mouse circuit 120 and the RS-232 serial port 112. In this case, a first cable 121 is used to connect the mouse 120 to the adapter 130, and then a second cable 131 is used to connect the adapter 130 to the RS-232 serial port 112. The adapter 130 is designed in such a manner that it can convert the PS/2 -compliant mouse data from the mouse 120 into RS-232-compliant format so that the mouse data from the mouse 120 can be accepted by the RS-232 serial port 112.
The foregoing example of FIGS. 1A-1B depicts a PS/2-compliant mouse which can be connected via an adapter to an RS-232 serial port. The adapter can be also designed to connect an RS-232-compliant mouse to a PS/2 port.
The foregoing solution, however, would not be universally usable on all the various makes of PCs. This problem arises from the fact that different manufacturers may use the undefined pins in the connecting port in different manners. For instance, there are two NC (No Connect) pins in the PS/2 port connector. In some PCs, these NC pins may be connected to the ground or used for the output of a periodic pulse train; while in some other PCs, these NC pins may be used for transmission of some other predefined signals. Therefore, the scheme of using the adapter 130 shown in FIGS. 1A-1B may allow the mouse to be connectable to some makes of PCs, but not universally to all makes.
Moreover, some notebook computers may be designed in such a manner that the output currents from the serial port are reduced in magnitude for the purpose of reducing power consumption. Since the power to drive mouse is typically fetched from the PC, the foregoing scheme would restrict the serial port to be used by some types of mouse devices that require large current to operate.
In conclusion, conventional mouse devices have the following drawbacks in utilization.
(1) First, conventional mouse devices can be connected to one type of connecting port only, either the RS-232 serial port or the PS/2 port, but not both. When purchasing a new mouse, the user needs to know which type of connecting port his/her PC supports. A wrong type of mouse can be purchased if the user is unaware of such distinctions.
(2) Second, conventional mouse converters would not allow the mouse to be universally usable on various makes of PCs.
(3) Third, conventional mouse devices that require large current to operate may not be usable on some notebook computers that supply a low current from the serial port.